error C5145: must write to gl_Position when creating shader program in open gl

I'm making a game engine right now, and I'm at the point of creating my first graphical object, though I'm encountering an error: when I run my program, the process of creating a shader program in open gl gives me this error:

error C5145: must write to gl_Position

Don't get me wrong on that: I found some stuff here and on other websites about the same problem, though the solutions don't work for me. They say I should write

glShaderSource(vertexShader, 1, &src, NULL);

instead of

glShaderSource(GL_VERTEX_SHADER, 1, &src, NULL);

(giving the method the, by me declared, unsigned int vertexShader instead of the by opengl defined macro GL_VERTEX_SHADER) but I still encounter the problem when writing it the "correct" way.

Here's my code for creating the shaders and linking the shader program:

vertex shader:

char* src = readShaderFile(path);

vertexShader = glCreateShader(GL_VERTEX_SHADER);
glShaderSource(vertexShader, 1, &src, NULL);
glCompileShader(vertexShader);

int  success;
char infoLog[512];
glGetShaderiv(vertexShader, GL_COMPILE_STATUS, &success);

if(!success)
{
    glGetShaderInfoLog(vertexShader, 512, NULL, infoLog);
    cout << "ERROR::SHADER::VERTEX::COMPILATION_FAILED\n" << infoLog << endl;
}
else
    cout << "vertex shader compiled" << endl;

fragment shader:

char* src = readShaderFile(path);

fragmentShader = glCreateShader(GL_FRAGMENT_SHADER);
glShaderSource(fragmentShader, 1, &src, NULL);
glCompileShader(fragmentShader);

int  success;
char infoLog[512];
glGetShaderiv(fragmentShader, GL_COMPILE_STATUS, &success);

if(!success)
{
    glGetShaderInfoLog(fragmentShader, 512, NULL, infoLog);
    cout << "ERROR::SHADER::FRAGMENT::COMPILATION_FAILED\n" << infoLog << endl;
}
else
    cout << "fragment shader compiled" << endl;

and shader program:

shaderProgram = glCreateProgram();
glAttachShader(shaderProgram, vertexShader);
glAttachShader(shaderProgram, fragmentShader);
glLinkProgram(shaderProgram);


int  success;
char infoLog[512];
glGetShaderiv(fragmentShader, GL_COMPILE_STATUS, &success);
glGetProgramiv(shaderProgram, GL_LINK_STATUS, &success);
if(!success) {
    glGetProgramInfoLog(shaderProgram, 512, NULL, infoLog);
    cout << "ERROR::SHADER::PROGRAM::LINKING::FAILED\n" << infoLog << endl; 
}
else
    cout << "shader program created" << endl;

the variables "vertexShader", "fragmentShader" and "shaderProgram" are unsigned ints

Note that the vertex shader and the fragment shader seem to compile just fine, since it doesn't "fail"